The role of covariate balance in observational studies

Observational data are prevalent in many fields of research, and it is desirable to use this data to make causal inferences. Because this data is nonrandom, additional assumptions are needed in order to construct unbiased estimators for causal effects. The standard assumption is strong ignorability, though it is often impossible to achieve the level of covariate balance that it requires. As such, researchers often settle for lesser balance levels within their datasets. However, these balance levels are generally insufficient to guarantee an unbiased estimate of the treatment effect without further assumptions. This article presents several extensions to the strong ignorability assumption that address this issue. Under these additional assumptions, specific levels of covariate balance are both necessary and sufficient for the treatment effect estimate to be unbiased. There is a trade‐off, however: as balance decreases, stronger assumptions are required to guarantee estimator unbiasedness. These results unify parametric and nonparametric adjustment methods for causal inference and are actualized by the Balance Optimization Subset Selection framework, which identifies the best level of balance that can be achieved within a dataset. © 2017 Wiley Periodicals, Inc. Naval Research Logistics 64: 323–344, 2017     

A Question of Escalation - From Counternarcotics to Counterterrorism: Analysing US Strategy in Colombia

This analysis addresses whether US strategy has escalated the ongoing conflict in Colombia. The study examines the ways in which US policy towards Colombia has been affected both by global circumstances after 9/11, and local events on the ground such as the involvement of private military firms which operate alongside multinational corporations in the country. The evidence suggests that US strategy has escalated the conflict, sometimes unintentionally, as the policy has evolved from an initial emphasis on countering the narcotics trade to one of counterterrorism. This has occurred, however, at the expense of other reforms, in particular by hindering the implementation of an effective pacification strategy. The analysis concludes that such an unbalanced strategy does not, as a consequence, provide for greater security and stability.     

Political opposition,external threats,and elite responses: analyzing domestic security policy in post-Rose Revolution Georgia

In the years since the 2003 Rose Revolution, the popularly elected leadership of the Republic of Georgia has responded to organized protests with a variety of repressive tactics. These reactions suggest that former challengers to authoritarian elites may utilize similar methods of retaining power during crisis periods. Yet, the alleged involvement of agencies of the Russian Federation in fomenting domestic instability has also occupied a central position in the national security policies of the outgoing Saakashvili government. These conditions both preceded and were reinforced by the South Ossetia War of August 2008. This article proposes a theoretical model that represents the intervening effect of interstate conflicts on state–society relations in Georgia from 2003 to present. It presents several hypotheses and possible indicators, data sources, and techniques for analyzing the interaction between characteristics of opposition groups, external threats, and the domestic security practices of contemporary Georgian political elites.     

Cyclic best first search: Using contours to guide branch‐and‐bound algorithms

The cyclic best‐first search (CBFS) strategy is a recent search strategy that has been successfully applied to branch‐and‐bound algorithms in a number of different settings. CBFS is a modification of best‐first search (BFS) that places search tree subproblems into contours which are collections of subproblems grouped in some way, and repeatedly cycles through all non‐empty contours, selecting one subproblem to explore from each. In this article, the theoretical properties of CBFS are analyzed for the first time. CBFS is proved to be a generalization of all other search strategies by using a contour definition that explores the same sequence of subproblems as any other search strategy. Further, a bound is proved between the number of subproblems explored by BFS and the number of children generated by CBFS, given a fixed branching strategy and set of pruning rules. Finally, a discussion of heuristic contour‐labeling functions is provided, and proof‐of‐concept computational results for mixed‐integer programming problems from the MIPLIB 2010 database are shown. © 2017 Wiley Periodicals, Inc. Naval Research Logistics, 64: 64–82, 2017     

IF YOU WANT IT DONE RIGHT,DO IT YOURSELF

Some have argued that the transatlantic rancor over the Iraq war made cooperation, especially on nonproliferation, unlikely. In contrast, this article, documents post-invasion instances of nonproliferation cooperation, with particular emphasis on the Proliferation Security Initiative and the EU-3 Initiative—the British, French, and German negotiations with Iran over its suspected nuclear activities. In addition to documenting French and British participation in these initiatives, the article analyzes why they have chosen to participate and argues that France and Britain have participated in both efforts because they are committed to avoiding future Iraq-like preventive wars.     

Game theory and the Second Iraq War

Throughout the world, there is a large number of young, and even not-so-young, scholars who are reading for higher degrees in strategic, security and defense studies, or engaged in analytical research in research institutes, think-tanks or consultancies; they bring to the subject innovative and fresh perspectives often ignored or missed by more established scholars. Most of these people have yet to make their mark in the defense and security field. The Editors of Defense & Security Analysis are resolved to tap this value source of information, observation, analysis and critical study by offering a new section of the journal for their views to be given an opportunity to be aired. Submissions of up to 3,000 words are encouraged from University Master's and Doctoral candidates and post-doctoral researchers.